Development and validation of a FRP-wrapped spiral corrugated tube for seismic performance of circular concrete columns

This paper presents the cyclic behavior of circular concrete columns confined with a proposed FRP-wrapped spiral corrugated tube (FWSCT) that serves as a permanent ribbed surface between FRP and concrete. Five FWSCT column specimens with GFRP layers and axial load ratios as design parameters were tested for the flexural and shear performances. The FWSCT specimens that did not use transverse steel hoops in the entire column used longitudinal reinforcement for the flexural capacity and FWSCT for the shear capacity. Specimen FWSCT-0 was confined with only a spiral corrugated steel tube without GFRP wraps; Specimens FWSCT-1, FWSCT-3, FWSCT-5 and FWSCT-8 were confined with a spiral corrugated steel tube and additional 1, 3, 5 and 8 GFRP layers, respectively. Test results showed that Specimen FWSCT-0 experienced shear failure at about 1% drift; Specimen FWSCT-1 experienced flexural shear failure at about 4% drift, while Specimens FWSCT-3, FWSCT-5 and FWSCT-8 exhibited rupture of longitudinal reinforcement at drift ratios of 7% to 8%, without shear failure. A plastic hinge was developed in un-wrapped column ends, further extending into the footing. An analytical method that used the residual shear model and a proposed plastic hinge length reasonably predicts the flexural and shear capacities of FWSCT columns.